This invention relates to a multi-functional vibration actuator generally mounted on a mobile communication apparatus, such as a mobile telephone, and having a function of generating a ringing tone or a speech sound in a sound mode and for generating tactile vibration in a vibration mode.
In a conventional multi-functional vibration actuator, a magnetic circuit comprising a yoke, a permanent magnet, and a plate is flexibly supported by a suspension comprising an arc-shaped helical leaf spring fixed to a vibration transmitting portion. The suspension of an arc shape has one end fixed to an outer periphery of the yoke of the magnetic circuit and the other end fixed to the vibration transmitting portion. The vibration actuator further comprises a vibrator member and a coil fixedly attached to a vibrator U-shaped portion of the vibrator member and is arranged in a gap within the magnetic circuit. As a consequence, the coil and the magnetic circuit are arranged on a single common axis. The vibrator U-shaped portion is formed at a desired position in a radial direction of the vibrator member. A lead wire for the coil is extracted outward from the vibrator member in a radial direction and is attached to an inner surface of an outer peripheral portion of the vibrator member through an elastic member such as an adhesive.
The outer peripheral portion of the vibrator member is fixed to the vibration transmitting portion. When the coil is applied with an a.c. driving current, the magnetic circuit or the coil moves towards or away from each other in an axial direction. The vibration transmitting portion serves as a fixed portion at a lower frequency and as an elastic member at a higher frequency to vibrate as a part of the vibrator member. In a vibration mode, the magnetic circuit and the coil attached to the vibrator member operate in reverse phases to transmit the vibration to the outside through the vibration transmitting portion.
In the structure of the conventional multi-functional vibration actuator, a distance between the vibrator member and each of one surface of the magnetic circuit and the suspension has a minimum value substantially equal to a distance between the other surface of the magnetic circuit and a cover faced thereto. If an amplitude of the movement of the magnetic circuit and the vibrator member is increased in the vibration mode, the magnetic circuit and/or the suspension may be brought into contact with the vibrator member to generate abnormal sound. Furthermore, depending upon the structure of the lead wire for the coil, the vibrator member may become unstable in operation in a sound mode. If an input driving voltage is increased or if the actuator is driven for a long time, the lead wire for the coil may be interrupted so that the actuator becomes inoperable.
It is therefore an object of this invention to provide a multi-functional vibration actuator in which a vibrator member is prevented from being brought into contact with a magnetic circuit and/or a suspension even if vibration of the vibrator member and the magnetic circuit is increased in a vibration mode and in which the vibrator member is stably operable in a sound mode.
According to this invention, there is provided a vibration actuator comprising a vibration transmitting portion forming a peripheral portion of the actuator, a magnetic circuit formed by the use of a permanent magnet, a vibrator member arranged at a distance from one surface of the magnetic circuit and having an outer periphery fixed to the vibration transmitting portion, a coil arranged in a gap within the magnetic circuit at a distance from the magnetic circuit and fixedly attached to the vibrator member, and a suspension fixed to the vibration transmitting portion and flexibly supporting the magnetic circuit, wherein the distance between the vibrator member and each of the one surface of the magnetic circuit and the suspension is greater than the distance between the other surface of the magnetic circuit and a cover covering the magnetic circuit.
Thus, the multi-functional vibration actuator of this invention has a structure such that the distance between the vibrator member and each of the one surface of the magnetic circuit and the suspension is greater than the distance between the other surface of the magnetic circuit and the cover. Furthermore, the vibrator member is formed in a shape such as a flat shape, a saucer shape, a curved shape, a corrugated shape, or a combination thereof with a desired radius of curvature such that a harmonic distortion component is minimized. With this structure, it is possible to avoid undesired contact between the magnetic circuit and the vibrator member around a resonance frequency in a vibration mode.
Preferably, the above-mentioned vibrator member is made of at least one kind of plastic film material selected from polyether imide (PEI), polyethylene terephthalate (PET), polycarbonate (PC), polyphenylenesulfide (PPS), polyarylate (PAR), polyimide (PI), and aramide (PPTA, poly-(paraphenylene terephthalamide)).
In the multi-functional vibration actuator of this invention, a lead wire for the coil fixedly attached to the vibrator member is laid on the surface of the vibrator member in a V shape, a U shape, a bellows-like shape, or a combination thereof and is attached to a desired point of the vibrator member by the use of an elastic member, such as an adhesive, applied in a spot-like fashion. Preferably, the lead wire is attached to a point on the outer periphery of the vibrator member. With this structure, an unstable operation of the vibrator member in a sound mode is suppressed to reduce distortion of a generated sound. In addition, it is possible to prevent a lead wire for the coil from being interrupted even if an input driving voltage of a high level is supplied and even if the actuator is driven for a long time.